There is certainly a fair amount of variability on re-administration with CogAT. I definitely have seen scores range widely over the years. The tests are in two-year bands, if I recall correctly, so that a certain number of items overlap from year to year, with the items pretty much turning over entirely by the time you get two years out. Keep in mind, also, regression to the mean and standard error. I believe I've linked this interesting article by the author of CogAT in the past:
https://faculty.education.uiowa.edu/docs/dlohman/Understanding_and_predicting_regression.pdfin this thread:
http://giftedissues.davidsongifted....sion_to_the_Mean_Why_tes.html#Post230897Backing up a moment on the question of syndromes existing/not existing, let's remember that there is no definitive physical/chemical/biological/imaging test for ASD, hyperlexia, or many other psychological/psychiatric disorders. We classify collections of symptoms in an attempt to impose our own order on the extreme diversity of human neurological development. I prefer to treat diagnostic categories as useful if they lead to improvements in the development, life functions, or personal understanding of the individual in question.
That being said, I think that hyperlexia, if it is defined specifically as fluent decoding without commensurate comprehension, may or may not overlap with giftedness, and may or may not overlap with ASD, but probably is less likely to overlap with giftedness, and more likely to overlap with some form of savantism, whether on the spectrum or otherwise. If it is defined as fluent decoding with or without commensurate comprehension, then, in the case of with comprehension, I think it is more likely to overlap with giftedness, with or without some other neurological/neuropsychological condition (such as a communication/language disorder, or ASD), and less likely to be solely a manifestation of ASD.
But that's just my opinion.
